If you ever used ZFS on a LUN and then tried to reuse that LUN for UFS you might have noticed a “weird” disk label on it. This is known as EFI label.
Here is how it looks in format command:
partition> p Current partition table (original): Total disk sectors available: 73383902 + 16384 (reserved sectors) Part Tag Flag First Sector Size Last Sector 0 usr wm 34 34.99GB 73383902 1 unassigned wm 0 0 0 2 unassigned wm 0 0 0 3 unassigned wm 0 0 0 4 unassigned wm 0 0 0 5 unassigned wm 0 0 0 6 unassigned wm 0 0 0 8 reserved wm 73383903 8.00MB 73400286
If you use straight format command there is no way to get rid of EFI label. Instead, you have to use -e option with format to get to expert features:
bash-3.00# format -e
With -e options when you label the LUN you will be asked about the type of label you want to put on the disk:
format> label  SMI Label  EFI Label Specify Label type: 0 Warning: This disk has an EFI label. Changing to SMI label will erase all current partitions. Continue? y Auto configuration via format.dat[no]? yes
I suppose you could alternatively use dd command and blank out the whole disk.